Vehicle wheel bearing apparatus is adapted to freely rotatably support a wheel hub to mount the wheel via a rolling bearing. It may include an inner ring rotation type for a driving wheel and both inner ring rotation and outer ring rotation types for a driven wheel. Double row angular ball bearings are widely used in such bearing apparatus since they have desirable bearing rigidity, high durability against misalignment, and small rotation torque required for fuel consumption. On the contrary double row tapered roller bearings are widely used for off-road vehicles, trucks and heavy duty vehicles.
The vehicle wheel bearing apparatus is broadly classified into a first, second, third or fourth generation structure. The first generation has a wheel bearing of double row angular contact ball type fit between a knuckle, forming part of a suspension, and a wheel hub. The second generation has a body mounting flange or a wheel mounting flange directly formed on the outer circumferential surface of an outer member. The third generation has one of the inner raceway surfaces directly formed on the outer circumferential surface of the wheel hub. The fourth generation structure has the inner raceway surfaces directly formed on the outer circumferential surfaces of the wheel hub and the constant velocity universal joint.
The vehicle wheel bearing apparatus with a double row tapered roller bearing apparatus is usually used in heavy duty vehicles such as trucks. Thus, it is not required to reduce the weight and size of the bearing apparatus. Accordingly, development of the double row tapered roller bearing apparatus has been stayed in use for the second generation structure as compared with the development of the double row angular ball bearing. However, since demand for wagon type vehicles has recently increased and thus multiple functions of vehicles are desired, it is desirable to reduce the weight and size in the double row tapered roller bearing apparatus having a large load capacity.
One example of a prior art wheel bearing apparatus is shown in FIG. 10. The vehicle wheel bearing apparatus 60 is formed by a double row tapered roller bearing having an outer member 61 with a body mounting flange 61b integrally formed on its outer circumferential surface. The body mounting flange 61b is mounted on a knuckle (not shown) of a vehicle. The outer member inner circumferential surface includes double row outer raceway surfaces 61a, 61a. An inner member 65 is integrally formed with double row inner raceway surfaces 62a, 64a on its outer circumferential surface arranged opposite to the double row outer raceway surfaces 61a, 61a. Double row tapered rollers 66, 66 are freely rollably contained between the outer raceway surfaces 61a, 61a and inner raceway surfaces 62a, 64a. Cages 67, 67 freely rollably hold the double row tapered rollers 66, 66.
The inner member 65 has a wheel hub 62 with a wheel mounting flange 63 integrally formed at one end. One inner raceway surface 62a is formed on the outer circumferential surface opposite to one of the double row outer raceway surfaces 61a, 61a. A cylindrical portion 62b axially extends from the one inner raceway surface 62a. A serration 62c, for torque transmission, is formed on the inner circumferential surface. An inner ring 64 is press fit onto the cylindrical portion 62b. The inner ring 62 is formed with the other inner raceway surface 64a on its outer circumferential surface opposite to the other of the double row outer raceway surfaces 61a, 61a. Thus, the inner member 65 forms a third generation wheel bearing apparatus structure for driving a driving wheel.
In addition, hub bolts 70 are adapted to be mounted on the wheel mounting flange 63 equidistantly along its outer periphery. Furthermore seals 68, 69 are mounted in annular openings formed between the outer member 61 and the inner member 65. The seals prevent leakage of grease contained within the bearing apparatus and entry of rain water or dusts into the bearing apparatus from the outside.
Large flanges 62d, 64b, for guiding the tapered rollers 66, are formed at larger side ends of the inner raceway surfaces 62a, 64a of wheel hub 62 and inner ring 64, respectively. However, no small flange is formed on the smaller side ends of the inner raceway surfaces 62a, 64a to prevent falling out of the tapered rollers. Accordingly, the cages 67 keep the tapered rollers 66 from a falling out condition by having the rollers 66 receiving pockets 71 in a pre-assembling condition. That is, as shown in FIG. 11, the cage 67 is formed of synthetic resin by injection molding. Posts 72 are formed between mutually adjacent pockets 71, 71 so that each of them has a trapezoidal cross section. Thus, the radially outward portion 72a is convergent tapered radially inward. A radially inward projection 72b is integrally formed with the post.
The width of a pocket 71 between the radially outward portions 72a, 72a is set so that the tapered roller 66 cannot radially outwardly fall out without it being contacted by the tapered surfaces of the posts 72. On the other hand, the width “W” between the radially inward projections 72b, 72b is set so that it is slightly smaller than the diameter of the tapered roller 66. Thus, each tapered roller 66 can be press fit radially inwardly into the pocket 71. Thus, it cannot inadvertently radially inwardly fall out since it is contacted by the radially inward projections 72b, as shown by a two-dot chain line. Accordingly, the cage structure 67 not only reduces the number of parts and manufacturing cost but makes it easy to assemble the bearing apparatus in an automatic assembling apparatus as well as eliminating assembling steps of the bearing apparatus (see Japanese Laid-open Patent Publication No. 44322/1999).